Rotary piston machine



July 21, 1936. o. ELWERT ROTARY PISTON MACHINE 2 Sheets-Sheet 2 Filed March 20, 1935 Fig. 4-

Patenkfi July 21, 1936 STATES" 'PATENT OFFICE Adolf Schniirle, Germany Stuttgart-Bad Cannstatt,

Application March 20, 1935, Serial No. 12,109 In Germany August 22, 1933 3 Claims.

This invention relates to a rotary piston machine of the Roots blower type, comprising two pistons rotating in opposite directions within a housing and making a sealing contact against each other, the pistons being positively interconnected by two gear wheels of equal diameter.

The purpose of the invention is to simplify and cheapen, without impairing the accuracy of manufacture of the rotary pistons, and to improve the 'efliciency and the output of the machine.

Rotary piston machines of this type heretofore generally had two similar rotary pistons with two or more teeth. The mutually contacting tooth faces were curved surfaces in the form of cycloids or. involutes, the manufacture of which is only possible by means of expensively formed cutters or hobs. The two faces of each tooth had to be individually made.

In accordance with the invention, one of the two pistons is made in the form of a perfectly flat plate with two parallel opposite sides which roll upon the opposite piston during the operation of the machine. The plate-shaped rotary piston is naturally very easy to produce accurately without using a copy ng or generating process. It requires a curved profile of the opposite piston, the production of which, in comparison with previously used tooth forms is simplified by the use of a tool having straight-working edges or a plane working face. Such a tool takes the place of the plate-shaped rotary piston. It is therefore possible, except for the narrow pockets in which the edges of the plate-shaped piston turn to work both sides of-a tooth in a continuous generating process.

The invention is illustrated by an example shown in the drawings, wherein:

Figure l'is a cross section through a rotary piston machine according to the invention;

Figure 2 is a longitudinal section through the same;

Figure 3 a transverse section of the pistons showing them in another position;

Figures 4 and 5 are fragmentary cross sectional views of a modified form of the piston in two different positions, and

Figure 6 is a sectional view transverse to a piston showing a milling cutter and illustrating the method of manufacture.

In Figures 1-3,- a plate-shaped rotary piston a having its axis at b, and an opposite piston c having its axis at d, are rotatably mounted in the usual manner at their two ends in a casing e. Two gear wheels I interconnecting the rotary pistons are shown in Figure 2 and their pitch circles indicated by dot and dash lines in Figs, 1 and 3.

The plate-shaped rotary piston a has. two entirely fiat sides 9. The narrow edges 7:. are rounded off in a cylindrical surface centered around the axis of rotation 12. The side walls 9 may be joined to the edges h by bevelled faces 7.

The opposite piston c has the profile required for mutual rolling of the pistons as they rotate at the same speed. The two rolling surfaces is are separated by two pockets m, in which the bev- 'elled oif edges of the plate-shaped rotary piston 11 engage, as shown in Figure 1. A sealing may take place at this point by the rolling of the cylindrical edges in on corresponding surfaces n in the pockets of the rotary piston c. The bevels a do not come into contact with the opposite piston, so that it is not necessary to finish the pockets except for the cylindrical surfaces n. Figure 3 shows a position of the rotary piston in which one side 9 of the plate-shaped piston u. is rolling along the rolling face k of the opposite pistons c.

As shown in Figures 4 and 5, there may be a construction of the rotary pistons in which there is absolutely no rolling or contact between the edges of the plate and the pockets of the rotary piston" c. Figure 4 shows the rotary pistons in their middle position. In Figure 5, that is after very slight turning, the rolling contact of the tooth faces begins again. The leakage losses are therefore practically insignificant. The last shown construction of the tooth faces has the advantage that the faces of the pockets can be cast to final shape and do not have to be finished.

If a more perfect sealing is desired during the turning of the edges of the plate in the pocket m, the simple bevels a may be replaced by a form corresponding to the usual gear wheel tooth.

In Figure 6, the machining of the rotary piston c by means of a face cutter o is represented. The cutting edges of the cutter all lie in a plane at right angles to the axis of rotation q. The feed motion of the rotary piston c with respect to the milling cutter is composed of a rotation around the axis d of the piston and a simultaneous displacement of the axis along a cylindrical path 1'. This motion is produced by the rolling of a toothed wheel .9 fixed upon the journal of the rot y piston upon a stationary toothed wheel t of the same size, whose axis is spaced from the working plane 1) of the' milling cutter by half the !thickness of'the plate-shaped rotary piston a. The rotary piston is mounted upon its journals in a revolving table.

Figure 6 shows the rotary piston c drawn out in one end position. Two other positions which occur during the milling process are shown in dot and dash lines. Instead of the milling cutter, there may be used a grinding wheel or a reciprocating planing tool whose straight cutting edge travels in the plane 11. There may also be substituted a process of manufacture in which the relative motions are obtained in reverse manner by holding the rotary piston stationary and imparting to the cutting tool the complementary machining motions. The rotary pistons can be cast in one piece with their Journals, or can be mounted upon shafts extending through them.

In order to attain as large a useful output as possible with the rotary piston machine, it is advantageous to give the plate-shaped rotary piston a greater width than the diameter of the interconnecting gear wheels.

The rotary piston machine according to the invention can be used as a blower for compressing or pumping air and gases, as well as for pumps for liquids. Conversely it can be used as a volumetric measuring device or as a power machine. r

I claim:

1. A rotary piston machine, comprising a casing enclosing a chamber. having two cylindrical pockets, an inlet, and an outlet; two oppositely rotating pistons in the respective pockets of said chamber, having mutually contacting rolling faces rigid therewith; and intermeshing gear wheels coaxialiy fixed to the respective pistons; one of said pistons being in the form of a fiat plate hav Z5 ing parallel opposite faces subtending arcs of substantially greater than ninety degrees on the pitch circle of the gear wheel to which the plateshaped piston is attached; the opposite one of said pistons having profile faces tangent to the respective flat faces of said plate-shaped piston in all positions of mutual contact.

' 2. A rotary piston machine, comprising a casing enclosing a chamber having two cylindrical pockets, an inlet, and an.outlet; two oppositely rotating pistons in the respective pockets of said chamber, having mutually. contacting rolling faces rigid therewith; and intermeshing gear wheels coaxialiyifixed to the respective pistons, one of said pistons being in the form of a flat plate having parallel opposite faces subtending 5 arcs of substantially greater than ninety degrees on the pitch circle of the gear wheel to which the plate-shaped piston is attached, the opposite one of said pistons having profile faces tangent to the respective fiat faces of said plate-shaped 10 piston in all positions of mutual contact, said opposite piston having reentrant pockets between saidprofile faces in which the edges of said plate-shaped piston turn, said edges and pockets having mutually contacting rolling .faces. 15

3. A rotary piston'machine, comprising a casing enclosing 'a chamber having two cylindrical pockets, an inlet, and an outlet; two oppositely rotating pistons in the respective pockets of said chamber, having mutually contacting rolling faces rigid therewith; and intermeshing gearwheels coaxially fixed to the respective pistons, one of said pistons being in the form of a flat plate having parallel opposite faces subtending arcs of substantially greater than ninety degrees 25.

on the pitch circle of the gear wheel to which the plate-shaped piston is attached, the opposite one of said pistons. having profile faces tangent to the respective fiat faces of said plate-shaped piston in all positions of mutual contact, said oppositepiston having reentrant pockets between said profile faces in which the edges of said plateshaped piston engage with play. 

